A continuing challenge in the semiconductor industry is to find new, innovative, and efficient ways of forming electrical connections with and between circuit devices which are fabricated on the same and on different wafers or dies. In addition, continuing challenges are posed to find and/or improve upon the packaging techniques utilized to package integrated circuitry devices.
One technique to alleviate these problems is optical waveguides through a wafer for signal interconnection of the front and back surfaces of a wafer. The optical waveguides include a highly reflective material that is deposited so as to clad an inner surface of the high aspect ratio holes which may be filled with air or a material with an index of refraction that is greater than one. Wave guiding is reflection at the interface of metal surrounding the core. These metal confined waveguides are used to transmit signals between functional circuits on the semiconductor wafer and functional circuits on the back of the wafer or beneath the wafer.
Another technique to address the above issues is to use optical fiber interconnects through a wafer for signal interconnection of the front and back surfaces of a wafer. This includes an integrated circuit with a number of optical fibers that are formed in high aspect ratio holes. The high aspect ratio holes extend through a semiconductor wafer. The optical fibers include a cladding layer and a core formed in the high aspect ratio hole. Wave guiding is provided by total internal reflection at the interface between the higher index of refraction core and the lower index of refraction of the material in which the guide is embedded. These optical fibers are used to transmit signals between functional circuits on the semiconductor wafer and functional circuits on the back of the wafer or beneath the wafer.
For signal interconnections over longer distances, for instance between different circuit die or modules, optical waveguides or fibers can be used. Previous approaches disclose a waveguide structure formed with a three-dimensional (3D) photonic crystal. The 3D photonic crystal comprises a periodic array of voids formed in a solid substrate. The voids are arranged to create a complete photonic bandgap. The voids may be formed using a technique called “surface transformation,” which involves forming holes in the substrate surface, and annealing the substrate to initiate migration of the substrate near the surface to form voids in the substrate. A channel capable of transmitting radiation corresponding to the complete bandgap is formed in the 3D photonic crystal, thus forming the waveguide. The waveguide may be formed by interfacing two 3D photonic crystal regions, with at least one of the regions having a channel. Alternatively a photonic crystal optical fiber made up of an array of conventional hollow core optical fibers may be employed. In this example, the array of optical fibers omits at least one fiber to form a central hollow core. The fiber works on the principle of two-dimensional photonic crystals to confine the radiation in a guided wave within the central hollow core. The fiber has a true photonic bandgap in which radiation of a particular energy or wavelength is totally forbidden, thereby providing a very high reflection coefficient to radiation incident the walls of the central hollow core over a select range of angles. The central hollow core allows for radiation propagation with minimal absorption.
In another approach, optical waveguides can be formed using rectangular or square strips of dielectric material embedded in a dielectric with a lower index of refraction. Wave guiding is provided by total internal reflection at the interface between the higher index of refraction core and the lower index of refraction of the material in which the guide is embedded. ZnO has been characterized for use as optical waveguides and directional amplified spontaneous ultraviolet emission near the bandgap energy has been observed from ZnO thin-film ridge waveguides for illumination (but not for signaling).